The compound 1,1,3-trioxo-1,2-benzothiazole-6-carboxamide of formula (I) is an important intermediate for preparing inter cilia the herbicidal agents such as mesosulfuron-methyl.

CN 103333120 describes a process for preparing mesosulfuron-methyl from p-toluic acid via the intermediate 1,2-benzisothiazole-6-carboxamide,2,3-dihydro-3-oxo-, 1,1-dioxide. Chromates which are hazardous reagents are used in the oxidation step.
CN 104610167 describes a process for preparing mesosulfuron-methyl which includes the steps of reduction of 6-nitrosaccharin to obtain 6-amino saccharin under a condition that reduction catalyst exists and diazotization of the 6-amino saccharin to obtain 6-isonitrosomethyl.
CN 103755603 describes the preparation of methyl-2-sulfamoyl-4-(methylsulfonamidomethyl)benzoate by the following steps: a reaction of p-(methylsulfonamidomethyl)toluene and chlorosulfonation agent (chlorosulfonic acid) at (−10)-0° C., and performing ammonolysis reaction in ammonia water at room temperature, to obtain 2-sulfamoyl-4-(methylsulfonamidomethyl)toluene; (2) oxidizing with potassium dichromate in concentrated sulfuric acid at (−4)-(−2)° C., to obtain 5-(methylsulfonamidomethyl)saccharin; and (3) dissolving in methanol, adding concentrated sulfuric acid, and performing alcoholysis reaction.
Based on the disadvantages in the above processes, it would be highly desirable to have an improved process for the production of the compound of formula (I) which is suitable for industrial use, highly efficient, low-cost, environmentally friendly, and provides a high yield in a relatively short reaction time, thereby overcoming the deficiencies of the prior art. The present subject matter provides such a process.
It is therefore a purpose of the present subject matter to provide a process that overcomes the disadvantages of the known art.